1. Field of the Invention
The present invention relates to a casing mechanism for electronic equipment and the like as well as to a medical imaging apparatus and ultrasound endoscope using the casing mechanism, where the casing mechanism contains circuit boards, board units, and the like mounted securely in a casing.
2. Description of the Related Art
Medical imaging apparatus such as ultrasound endoscope apparatus equipped with an ultrasound endoscope and the like have been put to practical use, where the ultrasound endoscope and the like is equipped, in a distal end portion of an insertion portion, with an ultrasound transducer which transmits and receives ultrasound waves and an image pickup device such as a photoelectric conversion device so that the insertion portion will be inserted in a body cavity for observation of organs and diagnosis.
Such a medical imaging apparatus contains electronic equipment made up of multiple circuit boards or board units mounted securely in a casing, where each board unit is made up of a circuit board and other relevant components. The circuit boards contain, for example, a control unit which controls driving of the ultrasound transducer, image pickup device, and the like of the ultrasound endoscope; a signal processing unit which performs various types of signal processing on an ultrasound signal, video signal, and the like received from the ultrasound endoscope; and other similar units, respectively.
As a means of electrically interconnecting multiple circuit boards in such electronic equipment, for example, a technique which interconnects the multiple circuit boards using a wire harness has been known previously.
FIG. 18 is a diagram showing an example of such a case. In FIG. 18, two circuit boards—a first circuit board 111 and second circuit board 121—are interconnected electrically by a wire harness 201 such as a flat cable.
On the other hand, as a means of electrically interconnecting multiple circuit boards without using a wire harness, a technique which uses connector members mounted on the circuit boards has been known previously.
FIG. 19 is a diagram showing an example of such a case. In FIG. 19, two circuit boards—a first circuit board 111A and second circuit board 121A—are equipped with a first connector member 114 and second connector member 124, respectively, and the two circuit boards 111A and 121A are interconnected electrically when the two connector members 114 and 124 are fitted together.
Thus, it is known that various means of connection have been available to interconnect multiple circuit boards.
However, in the case of a medical imaging apparatus such as an ultrasound endoscope apparatus, which has a large number of signal lines extending from a large number (hundreds) of ultrasound transducers and needs to ensure electrical connection of each signal line, the use of harness connection for electrical connection among the circuit boards will result in, for example, increased harness width, which may cause problems such as difficulty to form the harness and secure layout space and susceptibility to ambient noise. In particular, ultrasound signals handled by the ultrasound endoscope apparatus and the like are weak signals, which are susceptible to noise.
Thus, when electrically interconnecting multiple circuit boards and the like, a general tendency is to adopt means of connection which uses connector members to improve working efficiency and performance especially when there are a large number of connection wires.
In the case of electronic equipment in a medical imaging apparatus such as ultrasound endoscope apparatus, it is often the case that connector members are mainly used in a casing as a means of electrical connection among circuit boards as well as between circuit boards and board units.
In this case, the circuit boards, board units, and the like are configured to be replaceable by being mounted detachably in the casing. The use of connector members in interconnecting circuit boards or board units has the advantage of making attach/detach operations easier.
On the other hand, the electronic equipment in a medical imaging apparatus such as ultrasound endoscope apparatus requires a mechanism (hereinafter referred to as a casing mechanism) for screwing or otherwise fastening the circuit boards and board units in the casing. In this case, the casing mechanism generally has, for example, a sheet-metal structure.
Consequently, with the casing mechanism structured in this way, for example, depending on machining accuracy and the like, there can be misalignment between casing fasteners and board-side fastening locations (screw holes and the like) in the circuit boards which are fastened to the casing fasteners.
Also, the casing may be twisted depending on usage situations of the apparatus and external factors such as temperature changes. In that case, there can also be misalignment between the casing fasteners and board-side fastening locations.
To deal with the above situations, various measures have been proposed to absorb misalignment in the casing attributable to machining accuracy, external factors, and the like.
Now, let us consider a concrete configuration of a casing mechanism for electronic equipment in a medical imaging apparatus, where the casing mechanism is structured such as to electrically interconnect circuit boards, board units, and the like using connector members installed on the circuit boards and fasten the circuit boards and the like to casing fasteners with screws. FIG. 20 is a conceptual diagram showing a concrete example of such a case.
As shown in FIG. 20, the casing mechanism exemplified here is designed to fasten the circuit boards 111B and 121B to separate casing fasteners 131 and 132 with screws while ensuring electrical connection between two circuit boards 111B and 121B using connector members 114 and 124.
The casing mechanism configured as described above is assembled as follows. The second circuit board 121B is fastened to the second casing fastener 132, for example, at four locations using four screws 134. The second connector member 124 has been mounted on a mounting surface of the second circuit board 121B.
In this state, the first connector member 114 mounted on a mounting surface of the first circuit board 111B is fitted in the second connector member 124 of the second circuit board 121B. Consequently, the two circuit boards 111B and 121B are interconnected electrically.
In the state in which the two circuit boards 111B and 121B are interconnected via the connector members 114 and 124, the first circuit board 111B is fastened to the second circuit board 121B—which is fastened to the second casing fastener 132—only by means of the connector members 114 and 124. In this state, the first circuit board 111B is fastened to the first casing fastener 131, for example, at four locations using four screws 133.
Consequently, the first circuit board 111B is fastened to both the second circuit board 121B and first casing fastener 131.
In this way, the fit between the connector members 114 and 124 ensures electrical connection between the two circuit boards 111B and 121B while fastening the first circuit board 111B to the second circuit board 121B fastened to the casing fastener 132 in advance. Consequently, the first circuit board 111B is positioned with respect to the second circuit board 121B to begin with.
Next, in this state, the first circuit board 111B is screwed to the first casing fastener 131 to fasten the first circuit board 111B.
In the casing mechanism structured as described above, when the connector members 114 and 124 are fitted together, each fixing hole 111a formed in the first circuit board 111B and a corresponding screw hole 131a formed in the first casing fastener 131 must approximately align with each other.
However, there can be misalignment between the fixing holes 111a and screw holes 131a when the circuit board and casing are joined depending on accuracy and the like of drilling in the board and screw hole drilling in the casing.
In this case, when there is large misalignment between the fixing holes 111a and screw holes 131a, the screws 133 cannot be screwed into the screw holes 131a through the fixing holes 111a. On the other hand, when there is small misalignment between the fixing holes 111a and screw holes 131a, even if the screws 133 can be screwed into the screw holes 131a through the fixing holes 111a, loads are imposed on the fixing holes 111a, and thus on the first circuit board 111B when the screws 133 are screwed into the screw holes 131a. Consequently, loads are also imposed on the connector members 114 and 124.
Thus, by taking such misalignment into consideration, the fixing holes 111a in the first circuit board 111B fastened to the first casing fastener 131 with screws, for example, are made slightly larger in size to make some allowance.
That is, in the example shown in FIG. 20, since the fixing holes 111a are made slightly larger in diameter to make some allowance, when the screws 133 are passed through the fixing holes 111a and screwed into the screw holes 131a of the first casing fastener 131, the first circuit board 111B can be moved slightly along the mounting surface of the first circuit board 111B, i.e., in a direction perpendicular to a direction of screwing of the screws 133 until the screws 133 are tightened completely. However, since the first circuit board 111B has been fastened by means of the fit between the connector members 114 and 124, actually the first circuit board 111B cannot be moved, being fixed with respect to the second circuit board 121B as described above.
In short, the fixing holes 111a are made slightly larger to absorb misalignment between the fixing holes 111a and screw holes 131a. 
In this way, the casing mechanism shown in FIG. 20 ensures stability of electrical connection between the circuit boards 111B and 121B by setting reference mounting position of the first circuit board 111B to position of the connector members (114 and 124). Also, the casing mechanism absorbs misalignment between the fixing holes 111a in the first circuit board 111B and screw holes 131a in the first casing fastener 131 by making the fixing holes 111a slightly larger in diameter, and thereby prevents application of unnecessary loads on the connector members.
With the two circuit boards 111B and 121B interconnected securely by means of the connector members 114 and 124 and with the two circuit boards 111B and 121B fastened properly to the respective casing fasteners 131 and 132, desirably components are assembled without application of unnecessary loads on the connector members 114 and 124 or the circuit board itself.
However, with conventional casing mechanisms, it is common that mounting errors are caused by misalignment between circuit boards or between circuit boards and casing fasteners as described above and various measures have been devised by taking this situation into consideration.
For example, Japanese Patent Application Laid-Open No. 2001-94273 discloses a casing mechanism which is a cylindrical unit containing circuit boards. In order to prevent application of unnecessary loads on the circuit board even if the casing is twisted due to usage situations of the apparatus and external factors such as temperature changes, the circuit boards are placed being centered at a center axis of a cylindrical shape and are held by struts made of a material which elastically deforms in response to twisting of the casing.
Also, Japanese Patent Application Laid-Open No. 2000-315877 discloses a casing mechanism, wherein reinforcement members are placed in a casing to protect circuit boards from vibrations and shocks.
Furthermore, Japanese Patent No. 3302618 discloses a casing mechanism which contains board-clamping holders made of an elastically deformable material to elastically fasten circuit boards to casing fasteners.
Consequently, even under circumstances in which the circuit boards would be get shaky due to usage situations of the apparatus and external factors such as temperature changes, elastic deformation of the board-clamping holders absorb misalignment of mounting positions between the circuit boards and casing fasteners and thereby prevents connector members from being disconnected or causing loose connections.